The deal, signed by the General Administration of Quality Supervision, Inspection and Quarantine and its Brazilian counterpart on March 31, marks another step in Chinese efforts to diversify the suppliers of its corn imports, more than 90% of which currently comes from the U.S.

Under the agreement, China issued a quality permit for corn from the Latin American nation, formalizing an accord that Brazilian officials say was reached in November.

China has imported small amounts of Brazilian corn in the past, but such ...